Physics training: Poolgame

I made this poolgame for my "Applied Math & Physics" module. Aside from the physics aspect, it's also special because I tried to follow as many coding guidelines as feasable.

I used a mySQL database for this project.
In a real-life situation I would probably prefer XML
due to the small amount of data,
but I wanted to learn more about queries and databases in general.

I made the game framerate independent. That's quite essential for a physics game.

As said, this was also an exercise on following coding guidelines.
A good starting point for this is C++ Coding Standards by Sutter and Alexandrescu.
I used the Visitor design pattern for saving/loading.